Method for fabricating a nozzle

ABSTRACT

A system for machining a component with complex contour. The machining system includes a coolant flow nozzle with an interior passage with a first portion having a first cross-sectional shape, and a second portion having a second cross-sectional shape, with the second cross-sectional shape selected so that fluid discharged from the nozzle has a selected cross-sectional shape. A method of fabricating a coolant flow nozzle with an interior passage that has a varying cross sectional shape.

BACKGROUND OF THE INVENTION

This invention relates generally to methods and apparatus for machiningof components, such as gas turbine engine blades and vanes, which havecomplex contours.

Machining processes, such as grinding, for at least some knowncomponents discharge a coolant fluid toward the machining zone insufficient quantity and velocity to avoid heat damage to the machinedcomponent. However, when a complex profile is being machined in acomponent it may be difficult to provide adequate coolant to themachining zone along the entire profile because fluid flow that exitsthe nozzle diverges rapidly and may have insufficient velocity topenetrate the machining zone. Moreover, certain machining operations,such as grinding, may be limited to lower wheel speeds during machiningdue to lack of adequate cooling flows.

The present invention overcomes these difficulties by using a coolantflow nozzle that has an exit aperture for ejecting a fluid jet with aselected cross-sectional shape to substantially match the contour of thecomponent being machined. The fluid flow passage in the nozzle has afirst portion having a first cross-sectional shape, and a second portionhaving a second cross-sectional shape, wherein the secondcross-sectional shape is selected such that fluid discharged from thenozzle has a selected cross-sectional discharge pattern. The complexgeometry of the fluid flow passage in the nozzle can be machined byusing wire electro-discharge machine (“EDM”) techniques. The presentinvention facilitates providing enhanced cooling of the components withcomplex geometries during machining, leading to more accuracy andrepeatability of the machining process. The present invention alsoenables higher machining speeds to be utilized without creating thermaldamage to machined components, with longer tool life.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for fabricating a component, such as a nozzle,is provided. The method includes forming a specifically selectedcross-sectional shape for the exit aperture of the nozzle and forming aninlet aperture with another cross-sectional shape, such that a fluidpassage formed between the inlet and exit apertures transitionsgradually between the inlet cross-sectional shape and the exitcross-sectional shape. The complex geometry of the fluid flow passage inthe nozzle can be machined by using wire electro-discharge machine(“EDM”) techniques in which the two ends of the wire are independentlycontrolled in a computer numerical control (“CNC”) EDM machine.

A nozzle is provided for directing a cooling fluid towards a componentsuch as a gas turbine blade during machining. The nozzle includes a bodyincluding a first end, a second end, and a fluid passage extendingbetween the ends. The fluid flow passage in the nozzle has a firstportion having a first cross-sectional shape, and a second portionhaving a second cross-sectional shape, with the second cross-sectionalshape selected so that fluid discharged from the nozzle has a selectedcross-sectional shape.

A machining system is provided for machining a component, such as a gasturbine engine blade. The machining system includes a tool having anexterior shape suitable for machining the exterior shape of thecomponent, a mounting fixture that holds the component during machining,and a nozzle which has a fluid passage in it with a first portion havinga first cross-sectional shape, and a second portion having a secondcross-sectional shape, with the second cross-sectional shape selected sothat fluid discharged from the nozzle has a selected cross-sectionalshape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary gas turbine engine blade;

FIG. 2 is a schematic view of an exemplary machining tool assembly formachining a component, such as the gas turbine engine blade shown inFIG. 1;

FIG. 3 is a close up view of the machining tool assembly shown in FIG. 2showing the fluid jet discharged by the nozzle near the region ofmachining;

FIG. 4 is a perspective view of an exemplary nozzle that may be usedwith the machining tool assembly shown in FIG. 2;

FIG. 5 is a cross section of the starting block of material used to makethe nozzle shown in FIG. 4 by the wire Electro Discharge Machining (EDM)process; and

FIG. 6 is an exploded view of an alternative embodiment of the nozzlethat may be used with the machining tool assembly shown in FIG. 2,showing multiple parts of the nozzle.

DETAILED DESCRIPTION OF THE INVENTION

As used herein the terms “machining,” “machine,” and “machined” mayinclude any process used for shaping a component. For example, processesused for shaping a component may include turning, planing, milling,grinding, finishing, polishing, and/or cutting. In addition, and forexample, shaping processes may include processes performed by a machine,a machine tool, and/or a human being. The above examples are intended asexemplary only, and thus are not intended to limit in any way thedefinition and/or meaning of the terms “machining,” “machine,” and“machined”. In addition, as used herein the term “component” may includeany object that has been or may be machined. Furthermore, although theinvention is described herein in association with a gas turbine engine,and more specifically for use with engine blades and vanes for a gasturbine engine, it should be understood that the present invention maybe applicable to any component and/or any machining process.Accordingly, practice of the present invention is not limited to themachining of engine blades, vanes or other components of gas turbineengines. In addition, as used herein the term “machining apparatus” mayinclude any device used to machine a component.

FIG. 1 is a perspective view of an engine blade 10 that may be used witha gas turbine engine (not shown). In one embodiment, a plurality ofturbine blades 10 form a high-pressure turbine rotor blade stage (notshown) of the gas turbine engine. Each blade 10 includes an airfoil 12and an integral dovetail 14 that is used for mounting airfoil 12 to arotor disk (not shown) in a known manner. Alternatively, blades 10 mayextend radially outwardly from a disk (not shown), such that a pluralityof blades 10 form a blisk (not shown). Each airfoil 12 includes a firstcontoured sidewall 16 and a second contoured sidewall 18. First sidewall16 is convex and defines a suction side of airfoil 12, and secondsidewall 18 is concave and defines a pressure side of airfoil 12.Sidewalls 16 and 18 are joined at a leading edge 20 and at anaxially-spaced trailing edge 22 of airfoil 12. More specifically,airfoil trailing edge 22 is spaced chordwise and downstream from airfoilleading edge 20. First and second sidewalls 16 and 18, respectively,extend longitudinally or radially outward in span from a blade root 24positioned adjacent dovetail 14, to an airfoil tip 26.

FIG. 2 is a schematic view of an exemplary machining system 50 which maybe used for machining complex contours on aircraft engine components,such as blade 10 shown in FIG. 1. FIG. 3 shows a close up view of thenozzle coolant discharge region in the machining system shown in FIG. 2.In the exemplary embodiment shown in FIG. 2 and FIG. 3, machining system50 includes a grinding wheel 51, a component mounting fixture 52attached to a movable structure 56 and a nozzle 53. Grinding wheel 51 isdriven by a motor 54, and has a contoured shape that is variablyselected to create a desired contour on the component 55 being machined.The component is secured within the machining system using knowncomponent mounting fixtures 52, and coolant nozzle 53 is positioned todischarge a contoured jet of cooling fluid 54 towards component 55during machining. Although only one coolant nozzle 53 is shown in FIG. 2and FIG. 3, multiple coolant nozzles 53 can be used in the machiningsystem to discharge multiple jets of contoured coolant flow towardcomponent 55 during fabrication.

Cooling the workpiece during machining facilitates protecting theworkpiece from damage that may occur as heat is generated as a result ofmachining. Over time, continued exposure to the heat may cause thermalstresses, cracking, burning, and/or micro-structural damage to thecomponent. Although cooling fluids can be directed towards componentsusing tubes and simple shaped nozzles, it has been found that suchnozzles may be ineffective in preventing machining induced damage incomponents which have complex contours. Moreover, in such cases thecooling flow may not contact certain locations of the complex contour,resulting in damage at such locations. More specifically, there may beseveral reasons for their ineffectiveness. First of all, the coolingflow may not adequately reach the component location being machined dueto divergence of the fluid stream exiting from the nozzles. Anotherreason in the case of some machining processes, such as grinding, isthat a high rotational speed of the machining tool may induce airflownear the region of machining which disrupts the cooling flow jet awayfrom the component. This is particularly a problem with conventionalnozzles which may have to be positioned farther away from the componentdue to space limitations. In many cases, higher pressure for the coolingflow jet does not help to overcome these problems. Higher dischargepressures may actually result in more divergence and turbulence in thecooling flow stream from conventional cooling flow nozzles.

FIG. 4 illustrates a nozzle 53 which can overcome some of the problemswith conventional cooling nozzles described above. In the exemplaryembodiment, nozzle 53 is manufactured from a single piece block ofmaterial. FIG. 5 illustrates an example of an interior passage 90defined within nozzle 53. Nozzle 53 has a body 71, and two ends 72 and73, each of which may have different interior flow passage crosssectional shapes 91 and 92. Nozzle 53 also has an interior passage 90through which cooling fluid flows from inlet end 72 to exit end 73.Inlet end 72 includes means to attach it to external sources of supplyfor the cooling fluid. In the exemplary embodiment, inlet end 72 has acircular recess 93 which can accept the end of a cooling fluid supplytube 94 (shown in FIG. 3) for subsequent welding to nozzle 53. Exit endof interior passage 90 has a specific cross-sectional shape 91 which isgenerally similar to a portion of the component geometry to be machined,such as dovetail 14 (shown in FIG. 1).

FIG. 5 illustrates an exemplary shape of nozzle interior flow passage90. The cross-sectional shape 92 of interior passage 90 at inlet end 72is circular in the exemplary embodiment, although it can be of othercross-sectional shapes as well. The profile of passage 90 at inlet end72 is selected to substantively match that of connecting tubes 94 (shownin FIG. 3), or other structure supplying cooling fluid to the nozzle 53.A cross-sectional shape of flow passage 90 changes gradually from beingcircular near inlet end 72 to a selected shape 91 at a distance 98 fromexit end 73. There is a region 94 in the flow passage 90 near exit end73 in which the cross-sectional shape remains constant. A length 98 ofregion 94 near exit end 73 is selected to facilitate ensuring that flowemerging out of nozzle 53 does not diverge prior to impinging thecontour of the component being machined. There may also be a region 95(shown in FIG. 4) in the flow passage 90 near inlet end 72 in which thecross-sectional shape remains substantially constant. Region 95facilitates attaching nozzle 53 to external sources of cooling fluidsupply.

Pressurized cooling fluid enters the nozzle 53 at inlet end 72, andsince the cross-sectional area of nozzle 53 gradually decreases as thefluid traverses passage 90, the fluid is accelerated. The fluidacceleration continues to region 94 in passage 90 wherein thecross-sectional shape begins to remain constant. The region 94 ofsubstantially constant cross-section near exit end 73 facilitatesstraightening the coolant fluid flow, making it uniform and with reducedturbulence. Length 98 of region 94 near exit end 73 is typically tentimes the nominal thickness of the fluid jet profile.

One of the advantages of nozzle 53 is that the cooling fluid jet 54exiting nozzle 53 has a substantially uniform shape substantiallyselected to match a portion of the contour of the component 55 beingmachined. Moreover, this fluid jet 54 shape remains substantiallyuniform and with very little divergence. This is made possible byappropriately designing the internal passage geometry of the nozzle. Theshape and area of the nozzle exit aperture 91 is based on the profile tobe machined on the component 55, the tangential velocity of machiningtool 51, and the available volumetric flow of coolant. Morespecifically, the area of exit aperture 91 is selected such that thecoolant will cover the entire mass of material to be removed from thecomponent 55 and will exit nozzle 53 at a velocity that is substantiallyequal to or exceeding, the tangential velocity of the machine tool 51.Since the capacity of the cooling system is generally known, the exitvelocity is determined by dividing coolant flow rate by the area of theexit aperture 91.

The straight portion 94 of nozzle 53 facilitates producing anon-diverging stream from nozzle 53 into the machine zone (typically twoto ten inches away from the nozzle). In one embodiment, a length 98 is10 times the minor dimension of the exit aperture 91. For example, in anozzle with an exit aperture length of approximately 1.5 inches and witha width of approximately 0.050 inches the straight portion length isselected to be approximately 0.50 inches, and the coolant fluid velocityprofile will be adequately developed within nozzle 53. The inletaperture profile is then matched to the cross-sectional area of thetube, pipe, or fitting 94 (FIG. 3) that is delivering the coolant to thenozzle. This is normally a circular cross-section from a standard sizecomponent that has been chosen to fit into the geometric constraints ofthe overall machining system 50, but any shape can be accommodated bythe manufacturing method that is the subject of this invention.

From the cross-section of the inlet, the inlet area is calculated. Theinlet flow velocity can be calculated in the same manner as the exitflow because the volumetric flow is constant from the inlet to theoutlet of the nozzle. The required pressure at the inlet of the nozzlecan then be determined by applying standard fluid flow equations wellknown in the art. The length of the transition from the inlet aperture92 to the beginning of the straight portion 94 of the nozzle is thenselected based on the geometric limitations of machining system 50. Ingeneral, it is preferable to select the longest transition lengthavailable in order to generate a smooth flow. It is possible to obtaincooling flow rates of 25 gallons per minute per nozzle at velocities ofabout 65 meters/sec using cooling fluid pressures of about 318 psi. Thesmooth, uniform, contoured cooling flow jet 54 impinges the matchingcontour of the component being machined, providing cooling at alllocations along the contour of the component 55 in contact with themachining tool 51. Improved cooling at all locations of the contour ofthe component facilitates reducing heat damage to component 55 frommachining.

Another advantage of cooling nozzle 53 is that it can be located insidethe machining system 50 and farther away from the actual zone ofmachining. This is possible because the usual problem of divergence andturbulence of the cooling fluid jet stream from traditional nozzles hasbeen facilitated to be reduced by the invention that is the subjectmatter of this patent. The location of nozzle 53 relative to component55 and machine tool 51 eliminates the need to adjust the cooling nozzleseach time a tool needs to be changed and reduces machine set up time.This also enhances repeatability of the machining process to producecomponents of consistent quality by eliminating one source of variation.

Yet another advantage of the cooling flow nozzles which is the subjectof this patent is that because of their highly effective cooling ofcomponents during machining, they make higher material removal ratespossible. For example, in the grinding of aircraft engine components,with the use of coolant flow nozzles such as the ones described herein,it is possible to increase the grinding wheel tangential speeds and feedrates without any substantial heat damage to the components.

Yet another advantage of the cooling flow nozzles which is the subjectof this patent is that cooling of the components and machine tools usingthese highly effective cooling nozzles reduces the need to frequentlydress the profile of the grinding tools. The effective cooling of thegrinding wheel results in a reduction of the material removed from thegrinding wheel which reduces the frequency of grinding wheel dressingneeded. This reduces the machine set up time and increases tool life andproductivity.

FIG. 6 shows another alternative embodiment 80 of the cooling flownozzle assembly that may be used in the machining system 50 shown inFIG. 2. Nozzle assembly 80 is a two-piece design which has a top piece81 and a bottom piece 82. Each piece has features 83 and 84 machinedthereon which enables them to be assembled together into a single nozzle53. Each piece 81 and 82 defines a portion of the interior flow passage85 and 86 machined into it. The two pieces 81 and 82 are machinedseparately and are later assembled together to form a nozzle as shown inFIG. 4. Once assembled, the cooling flow nozzle assembly 80 functionsexactly as described previously.

The cooling fluid flow path inside the nozzle 53 can be manufactured byany suitable conventional or non-conventional machining process. Oneparticularly convenient way to make the nozzles is by electro-dischargemachining. A block of any suitable material 96 (FIG. 5), such asstainless steel, high carbon steel or hardened steel is first made. Astarter hole (not shown) is then drilled through the block 96. Anelectro-discharge machine (“EDM”) tool wire 97 is inserted through thestarter hole in the block. Electro-discharge machining is then performedalong the entire length of the block to create the shape of the profile91 at the exit end 73 of the nozzle. This is accomplished by using acomputer numerical control (“CNC”) EDM machine in which both ends of theEDM wire 97 are guided to follow the two-dimensional contour of the exitprofile 91 of the nozzle. The inlet profile 92 (FIG. 5) at the inlet end72 of the nozzle and the gradual transition from the exit profile to theinlet profile is then created by using the CNC EDM machine. This isaccomplished by independently controlling the path traversed by the twoends of the EDM wire tool where the EDM wire at the inlet end followsthe inlet contour 92 of the nozzle and the end of the EDM wire at theexit end follows contour 91 at a location which is located a distance 98from the exit end 73 of the nozzle.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method for fabricating a nozzle including at least one piece, saidmethod comprising: forming at least a portion of an exit aperture in atleast one piece of the nozzle, wherein the at least a portion of theexit aperture has a first cross-sectional shape configured to dischargea fluid with a shape that substantially matches a portion of a contourof a component to be fabricated using the nozzle; and forming at least aportion of an inlet aperture in the at least one piece of the nozzle,wherein the at least a portion of the inlet aperture has a secondcross-sectional shape, and such that a fluid passage formed between theinlet and exit apertures transitions gradually between the firstcross-sectional shape and the second cross-sectional shape.
 2. A methodin accordance with claim 1 wherein forming at least a portion of an exitaperture further comprises forming at least a portion of the exitaperture using an electro-discharge machining process.
 3. A method inaccordance with claim 1 wherein forming at least a portion of an inletaperture further comprises forming the fluid passage using anelectro-discharge machining process.
 4. A method in accordance withclaim 1 wherein forming at least a portion of an exit aperture furthercomprises extending a portion of the exit aperture along an axial lengthof the nozzle such that the second cross-sectional shape remainssubstantially constant for a distance.
 5. A method in accordance withclaim 1 further comprising forming a starter hole within a piece ofstock material prior to forming the at least a portion of the exitaperture.
 6. A method in accordance with claim 1 further comprisingcoupling a first piece of the nozzle to a second piece of the nozzle.7.-20. (canceled)